Sometimes a dispatcher or an admin may need to complete a route on behalf of a driver. It may happen when a driver hasn't completed his route (completed all tasks but failed to tap the 'End Route' button in his driver app) and is not available the next day or several days after the route was executed.
In this situation, you can select this route and click on three dots in the upper right of the Assignments sections, and select Complete route from the dropdown. In the pop up that will show up, you may additionally select the exact time when you would like the route should be ended. When done click Confirm - the route will be moved to Done and will be considered as completed.